CN105121684A - Hot-rolled steel sheet and method for manufacturing same - Google Patents
Hot-rolled steel sheet and method for manufacturing same Download PDFInfo
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- CN105121684A CN105121684A CN201480019788.9A CN201480019788A CN105121684A CN 105121684 A CN105121684 A CN 105121684A CN 201480019788 A CN201480019788 A CN 201480019788A CN 105121684 A CN105121684 A CN 105121684A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 191
- 239000010959 steel Substances 0.000 title claims abstract description 191
- 238000000034 method Methods 0.000 title claims abstract description 34
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 48
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 47
- 239000000203 mixture Substances 0.000 claims abstract description 32
- 239000012535 impurity Substances 0.000 claims abstract description 13
- 238000001816 cooling Methods 0.000 claims description 94
- 238000005496 tempering Methods 0.000 claims description 38
- 238000005096 rolling process Methods 0.000 claims description 37
- 229910052748 manganese Inorganic materials 0.000 claims description 25
- 229910052720 vanadium Inorganic materials 0.000 claims description 23
- 229910052799 carbon Inorganic materials 0.000 claims description 22
- 229910052750 molybdenum Inorganic materials 0.000 claims description 22
- 229910052759 nickel Inorganic materials 0.000 claims description 21
- 229910052758 niobium Inorganic materials 0.000 claims description 18
- 229910052804 chromium Inorganic materials 0.000 claims description 17
- 238000001556 precipitation Methods 0.000 claims description 17
- 229910052802 copper Inorganic materials 0.000 claims description 16
- 230000008569 process Effects 0.000 claims description 15
- 229910052719 titanium Inorganic materials 0.000 claims description 15
- 238000009749 continuous casting Methods 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
- 238000001953 recrystallisation Methods 0.000 claims description 5
- 229910000859 α-Fe Inorganic materials 0.000 abstract description 53
- 239000000463 material Substances 0.000 abstract description 6
- 239000000126 substance Substances 0.000 abstract 1
- 239000002344 surface layer Substances 0.000 abstract 1
- 238000010276 construction Methods 0.000 description 30
- 230000006866 deterioration Effects 0.000 description 24
- 238000012360 testing method Methods 0.000 description 22
- 238000005516 engineering process Methods 0.000 description 18
- 230000009466 transformation Effects 0.000 description 18
- 239000002994 raw material Substances 0.000 description 17
- 238000003303 reheating Methods 0.000 description 17
- 230000000694 effects Effects 0.000 description 16
- 238000005098 hot rolling Methods 0.000 description 13
- 238000005204 segregation Methods 0.000 description 8
- 229910001566 austenite Inorganic materials 0.000 description 7
- 230000007704 transition Effects 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 6
- 230000033228 biological regulation Effects 0.000 description 6
- 239000013078 crystal Substances 0.000 description 6
- 238000000605 extraction Methods 0.000 description 6
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 6
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 6
- 238000010521 absorption reaction Methods 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000005266 casting Methods 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 230000005611 electricity Effects 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 230000006698 induction Effects 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 230000008520 organization Effects 0.000 description 4
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 230000000007 visual effect Effects 0.000 description 4
- 238000003466 welding Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000009863 impact test Methods 0.000 description 3
- 239000003345 natural gas Substances 0.000 description 3
- 239000003129 oil well Substances 0.000 description 3
- 235000019362 perlite Nutrition 0.000 description 3
- 239000010451 perlite Substances 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 235000009508 confectionery Nutrition 0.000 description 2
- 238000005868 electrolysis reaction Methods 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000010191 image analysis Methods 0.000 description 2
- 238000004020 luminiscence type Methods 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 238000011002 quantification Methods 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- QEMXHQIAXOOASZ-UHFFFAOYSA-N tetramethylammonium Chemical compound C[N+](C)(C)C QEMXHQIAXOOASZ-UHFFFAOYSA-N 0.000 description 2
- 238000007669 thermal treatment Methods 0.000 description 2
- 229910018643 Mn—Si Inorganic materials 0.000 description 1
- YRKCREAYFQTBPV-UHFFFAOYSA-N acetylacetone Natural products CC(=O)CC(C)=O YRKCREAYFQTBPV-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000007542 hardness measurement Methods 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- OKKJLVBELUTLKV-UHFFFAOYSA-N methyl alcohol Substances OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 1
- -1 methyl ethyl Chemical group 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- TZMFJUDUGYTVRY-UHFFFAOYSA-N pentane-2,3-dione Chemical compound CCC(=O)C(C)=O TZMFJUDUGYTVRY-UHFFFAOYSA-N 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/001—Heat treatment of ferrous alloys containing Ni
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
- Metal Rolling (AREA)
- Soft Magnetic Materials (AREA)
Abstract
Provided are: a hot-rolled steel sheet which is suitable as a material for a X80-grade electric resistance welded steel pipe or a material for a X80-grade spiral steel pipe and has excellent strength, toughness and elongation properties; and a method for manufacturing the hot-rolled steel sheet. A hot-rolled steel sheet having high strength and excellent toughness and ductility, which has a chemical composition comprising, in mass%, 0.04 to 0.15% inclusive of C, 0.01 to 0.55% inclusive of Si, 1.0 to 3.0% inclusive of Mn, 0.03% or less of P, 0.01% or less of S, 0.003 to 0.1% inclusive of Al, 0.006% or less of N, 0.035 to 0.1% inclusive of Nb, 0.001 to 0.1% inclusive of V, 0.001 to 0.1% inclusive of Ti and a remainder made up by Fe and unavoidable impurities, wherein the ratio of the amount of precipitated Nb relative to the whole amount of Nb is 35 to 80% inclusive, the volume fraction of a tempered martensite and/or a tempered bainite each having a Las interval of 0.2 to 1.6 [mu]m inclusive is 95% or more at a position located at a depth of 1.0 mm from the surface layer of the steel sheet as observed in a thickness direction, and the volume fraction of a ferrite having a Las interval of 0.2 to 1.6 [mu]m inclusive is 95% or more at a center position of the steel sheet as observed in a thickness direction.
Description
Technical field
The present invention relates to and have high strength and low-temperature flexibility and ductility also excellent de hot-rolled steel sheet and manufacture method thereof, described hot-rolled steel sheet is applicable to the raw material of the steel pipe used in pipeline (pipeline), oil well pipe (OilCountryTubularGoods), civil construction (civilengineeringandconstruction) use etc., is specially adapted to the raw material of API (AmericanPetroleumInstitute) specification X80 level steel pipe.
The application based on the Japanese Patent Application 2013-078395 CLAIM OF PRIORITY of on April 4th, 2013 in Japanese publication, and here cites its content.
Background technology
In recent years, owing to increasing energy requirement, so the transport efficiency in order to improve Sweet natural gas (naturalgas), oil, for line pipe, just progressively use can the high strength of withstand high pressures operation (high-pressureoperation), large footpath and heavy wall steel pipe (heavywallsteelpipe).For this requirement, mainly having used with slab is in the past the UOE steel pipe of raw material.But, recently, in order to reduce the construction cost of pipeline, solve the supply capacity deficiency etc. of UOE steel pipe, and also strong to the requirement of the reduction raw materials cost of steel pipe, thus start to use gradually high and more inexpensive with UOE steel pipe phase specific production rate, be that the electricity of raw material stitches steel pipe (electricresistanceweldedsteelpipeortube), Spiral Steel Pipe (spiralsteelpipe) with hot-rolled steel sheet.
At this, because pipeline is laid on the abundant cold district (coldweatherregion) of the reserve of such as Sweet natural gas mostly, therefore for line pipe material steel plate, certainly to require high strength, but also require that low-temperature flexibility (low-temperaturetoughness) is excellent.In addition, electricity seam steel pipe or Spiral Steel Pipe were widely used in automotive part (automotivemember), steel pipe piling (steelpipepile) etc. in the past, and usually with the thinner hot-rolled steel sheet of thickness of slab for raw material.But, when requiring the steel pipe of heavy wall, hot-rolled steel sheet that thickness of slab compared with the past is thicker must be used as raw material.When steel plate thicker for thickness of slab is manufactured pipe, for the line pipe that particularly harsh for the processing conditions in the territory, thickness of slab top layer of steel plate and long distance is laid, the possibility of the imposed deformation that the diastrophism (crustalchange) being likely subject to earthquake etc. causes, so as the hot-rolled steel sheet of line pipe raw material, not only require desired intensity and low-temperature flexibility, also must have the stretch characteristics of the total thickness that can tolerate processing as described above and distortion concurrently.
In such a case, various technology is proposed about the hot rolling raw material of line-pipes at present.
Such as, propose following technology in patent documentation 1, namely, propose a kind of high strength electricity slit-tube hot rolled strip, by hot rolled strip being formed as the following composition formed, namely in mass % containing C:0.005 ~ 0.04%, Si:0.05 ~ 0.3%, Mn:0.5 ~ 2.0%, Al:0.001 ~ 0.1%, Nb:0.001 ~ 0.1%, V:0.001 ~ 0.1%, Ti:0.001 ~ 0.1%, below P:0.03%, below S:0.005% and below N:0.006%, and containing being selected from below Cu:0.5%, one or two or more kinds in below Ni:0.5% and below Mo:0.5%, remainder is Fe and inevitable impurity, meeting the Pcm represented by formula Pcm=[%C]+[%Si]/30+ ([%Mn]+[%Cu])/20+ [%Ni]/60+ [%Mo]/7+ [%V]/10 is less than 0.17 form, by making the ratio of the organization formation of hot rolled strip shared by the bainite ferrite (bainiticferrite) as principal phase in total tissue be the tissue of more than 95vol%, thus make low-temperature flexibility and weldability (weldability) excellence.
Following technology is proposed in patent documentation 2, namely, a kind of heavy wall high tensile hot-rolled steel sheet, by the composition of hot-rolled steel sheet being formed as the following composition formed, namely in mass % containing C:0.02 ~ 0.08%, Si:0.01 ~ 0.50%, Mn:0.5 ~ 1.8%, below P:0.025%, below S:0.005%, Al:0.005 ~ 0.10%, Nb:0.01 ~ 0.10%, Ti:0.001 ~ 0.05%, and to make C, Ti, Nb meets ([%Ti]+([%Nb]/2))/[%C] < 4, remainder is Fe and inevitable impurity, the organization formation of hot-rolled steel sheet is that being positioned at from surface of steel plate to the average crystal grain footpath of the ferritic phase as principal phase of the position of thickness of slab direction 1mm and the poor Δ D in average crystal grain footpath of the ferritic phase as principal phase of the thickness of slab middle position being positioned at steel plate is less than 2 μm, and be positioned at from surface of steel plate to the tissue point rate (volume %) of the second-phase of the position of thickness of slab direction 1mm and the poor Δ V of tissue point rate (volume %) of second-phase of the thickness of slab middle position being positioned at steel plate be less than 2%, be positioned at from surface of steel plate to the minimum lath interval (minimumlathinterval) of the Bainite Phases of Some (bainitephase) of the position of thickness of slab direction 1mm or tempered martensite phase (temperedmartensitephase) be more than 0.1 μm, form the heavy wall high tensile hot-rolled steel sheet of the uniform in material excellence in low-temperature flexibility and thickness of slab direction thus.
Patent documentation 3 proposes following technology, namely, a kind of hot-rolled steel sheet, by the composition of hot-rolled steel sheet being formed as the following composition formed, namely in mass % containing C:0.03 ~ 0.06%, below Si:1.0%, Mn:1 ~ 2%, below Al:0.1%, Nb:0.05 ~ 0.08%, V:0.05 ~ 0.15%, Mo:0.10 ~ 0.30%, remainder is Fe and inevitable impurity, and be that Bainite Phases of Some is single-phase by the organization formation of hot-rolled steel sheet, and the carboritride of Nb and V forms with total metering conversion score loose more than 0.06% of Nb and V in this Bainite Phases of Some, form the hot-rolled steel sheet having the intensity of more than tensile strength TS:760MPa and the toughness of fracture transition temperature (fracturetransitiontemperature) less than vTrs:-100 DEG C concurrently thus.
In addition, about the technology relating to the Plate Steel different from hot-rolled steel sheet, following technology is proposed: by the composition of steel plate being formed as the following composition formed in patent documentation 4, namely in mass % containing C:0.06 ~ 0.12%, Si:0.01 ~ 1.0%, Mn:1.2 ~ 3.0%, below P:0.015%, below S:0.005%, below Al:0.08%, Nb:0.005 ~ 0.07%, Ti:0.005 ~ 0.025%, below N:0.010%, below O:0.005%, remainder is Fe and inevitable impurity, and be made up of the organization formation of steel plate bainite and island-like martensite (M-AConstituent) 2 phase constitution, the Line Integral rate of this island-like martensite is 3 ~ 20% and diameter of equivalent circle is less than 3.0 μm, display low yield strength ratio can be formed thus and the high tensile steel plate of the uniform stretch characteristics of excellence.
In addition, following technology is proposed in patent documentation 5, a kind of i.e. method manufacturing heavy wall high tensile hot-rolled steel sheet, hot-rolled steel sheet is implemented to the accelerating cooling be made up of an accelerating cooling and secondary accelerating cooling, one time accelerating cooling carries out as follows: the average cooling rate carrying out thickness of slab central position is 10 DEG C/more than s, and the average cooling rate of thickness of slab central position and the cooling being less than 80 DEG C/s from surface of steel plate to the speed of cooling difference of the average cooling rate of the position of thickness of slab direction 1mm, until become the once cooling stopping temperature of the temperature of the temperature field of less than 650 DEG C more than 500 DEG C to the temperature of the position of thickness of slab direction 1mm from surface of steel plate.Above-mentioned secondary accelerating cooling carries out as follows: the average cooling rate carrying out thickness of slab central position be 10 DEG C/more than s and the average cooling rate of thickness of slab central position with from surface of steel plate to the cooling that the speed of cooling difference of the average cooling rate of the position of thickness of slab direction 1mm is 80 DEG C/more than s, until the temperature of thickness of slab central position is BFS (DEG C)=770-300C-70Mn-70Cr-170Mo-40Cu-40Ni-1.5CR (CR: speed of cooling (DEG C/s)) cooling twice below stop temperature.After this secondary accelerating cooling, reel with the coiling temperature of the temperature of thickness of slab central position for BFS0 (DEG C)=below 770-300C-70Mn-70Cr-170Mo-40Cu-40Ni, manufacture the heavy wall high tensile hot-rolled steel sheet of strength ductile balancing good thus, the steel raw material formation composed as follows of described hot-rolled steel sheet, namely in mass %, containing C:0.02 ~ 0.08%, Si:0.01 ~ 0.50%, Mn:0.5 ~ 1.8%, below P:0.025%, below S:0.005%, Al:0.005 ~ 0.10%, Nb:0.01 ~ 0.10%, Ti:0.001 ~ 0.05%, and C, Ti, Nb meets ([%Ti]+([%Nb]/2))/[%C] < 4, remainder is that Fe and inevitable impurity are formed, the hot rolling implementing to be made up of roughing and finish rolling to the steel raw material so formed is to form hot-rolled steel sheet.
Look-ahead technique document
Patent documentation
Patent documentation 1: Japanese Unexamined Patent Publication 2004-315957 publication
Patent documentation 2: Japanese Unexamined Patent Publication 2010-196157 publication
Patent documentation 3: Japanese Unexamined Patent Publication 2011-17061 publication
Patent documentation 4: Japanese Unexamined Patent Publication 2011-94230 publication
Patent documentation 5: Japanese Unexamined Patent Publication 2010-196163 publication
Summary of the invention
But, in above-mentioned prior art, all be difficult to the hot-rolled steel sheet obtaining being suitable as line-pipes raw material, namely there is high strength and the thick hot-rolled steel sheet of the low-temperature flexibility also excellent and harsh processing conditions that has concurrently when can tolerate tubing and the sufficient ductility because of the caused compulsory distortion such as the diastrophism after laying.
In the technology proposed in sharp document 1, as shown in embodiment, due to the speed of cooling after hot rolling is terminated control for 20 DEG C/below s formed desired hot rolled strip tissue (as principal phase bainite ferrite shared by ratio be the tissue of more than 95vol%), so there is following problem, namely, easily cause the coarsening of the lath in bainite ferrite, intensity (particularly tensile strength) easily reduces.In addition, in the technology proposed in patent documentation 1, in order to ensure hardening capacity, to need to add in Cu, Ni, Mo any one more than a kind.But these elements are rare elements, can hinder later stably manufactured, so not preferably as bioelement.
In the technology proposed in patent documentation 2, in order to form desired hot-rolled steel sheet tissue, after hot rolling terminates, need to be implemented as follows cooling: be 100 DEG C/more than s with the average cooling rate from surface of steel plate to the position of thickness of slab direction 1mm and the average cooling rate of thickness of slab middle position is the cooling of 10 DEG C/more than s.Like this, in the technology of speed of cooling improving plate near surface, if particularly thickness of slab is thickening, then the speed of cooling on plate surface becomes too fast, and as a result, surface hardness becomes too high, there is the problem of the extensibility reduction under total thickness and so on.
As described above, as line-pipes material, the stretch characteristics of intensity, low-temperature flexibility and total thickness is particularly important.But, when thick hot-rolled steel sheet, if want after hot rolling terminates, make thickness of slab middle position guarantee the speed of cooling specified, then will extremely increase in the speed of cooling in territory, thickness of slab top layer.Its result, the high rigidityization in territory, thickness of slab top layer is remarkable, and the stretch characteristics thereupon under total thickness reduces.The problem of the stretch characteristics deterioration under total thickness, especially significantly changes along with the carrying out of high strength in recent years, and the stretch characteristics so under total thickness reduces, then tubing processing becomes extremely difficult.In addition, when carrying out constructing as line pipe, the imposed deformation caused because of earthquake etc. and likely cause Serious Accident.
For the technology proposed in patent documentation 3, in order to form desired hot-rolled steel sheet tissue, after hot rolling terminates, need the temperature field being cooled to 550 ~ 650 DEG C in thickness of slab central authorities with the average cooling rate of 20 DEG C/more than s.The technology that the technology particularly proposed in patent documentation 3 is is object with the hot-rolled steel sheet of the so very high intensity of more than TS:760MPa, so when thickness of slab thickens, especially the hardness in territory, plate top layer is easily caused to rise, the problem of the stretch characteristics deterioration under total thickness.
For such problem, in the technology proposed in patent documentation 4, by being formed in Bainite Phases of Some the tissue making island-like martensite fine uniform structure disperse, the uniform extension characteristic (uniformelongationproperty) of high tensile steel plate can be guaranteed.But, in the technology proposed in patent documentation 4, need the island-like martensite containing more than 3%, have the problem easily causing toughness (particularly DWTT characteristic (dropweightteartestproperty)) deterioration.In addition, in order to ensure above-mentioned tissue, it is characterized in that, after carrying out hot rolling, carry out cooling make steel plate medial temperature until 500 ~ 680 DEG C, carry out immediately thereafter reheating until more than 550 DEG C and cooling starts below temperature.But, in order to make the medial temperature of steel plate rise, in fact also existing and needing reheating equipment etc. to arrange and the problem to complicate and so on of manufacturing process.
In addition, in the technology proposed in patent documentation 5, in process of cooling after hot rolling terminates, by making the average cooling rate of thickness of slab central position be less than 80 DEG C/s with the speed of cooling difference of the average cooling rate from surface of steel plate to the position of thickness of slab direction 1mm, thus guarantee the strength ductile balance of heavy wall high tensile hot-rolled steel sheet.But, as line pipe, oil well pipe and civil construction raw materials requirement high, in heavy wall material more than thickness of slab 1 inch (25.4mm), in order to the average cooling rate of thickness of slab central position and the speed of cooling difference from surface of steel plate to the average cooling rate of the position of thickness of slab direction 1mm are controlled as being less than 80 DEG C/s and being cooled to the temperature of regulation, there are the following problems: need the transporting velocity (transportationvelocity) that configures cooling tank (coolingbanks) in a large number or delay steel plate and extend cooling time, so, productivity reduces, need to set up new equipment.
The present invention completes in order to the problems referred to above solving prior art and exist, and its object is to provide hot-rolled steel sheet and the manufacture method thereof of the stretch characteristics excellence under a kind of intensity, toughness and the total thickness that are applicable to X80 level electricity seam steel pipe raw material or X80 level Spiral Steel Pipe raw material.
The present inventor etc. are the thick hot-rolled steel sheet of more than 12mm about such as thickness of slab, and to not adding the rare elements such as Cu, Ni, Mo just can guarantee high strength, high tenacity as far as possible, the means simultaneously improving the stretch characteristics under total thickness conduct in-depth research.
First, the present inventor etc. are studied following means: be conceived to the ferrite of toughness and ductility excellence, tempered martensite and tempering bainite, be organized as the principal phase of hot-rolled steel sheet with these, thus do not add the strengthening elements such as Cu, Ni, Mo and just can guarantee hot-rolled steel sheet intensity.
Its result, have following opinion: ferrite also exists the ferrite with panel construction (lathstructure), such ferrite with panel construction manifests the phase transformation strengthening (transformationstrengthening) being spaced apart governing factor with lath.
Ferritic panel construction cannot pass through opticmicroscope (opticalmicroscope) to be observed, and can pass through transmission type microscope (transmissionelectronmicroscope) (TEM) or sweep electron microscope (scanningelectronmicroscope) (SEM) and carry out structure observation (multiplying power: 5000 ~ 20000 times) and confirm.Should illustrate, such panel construction can be observed in tip-like ferrite (acicularferrite) and bainite ferrite (bainiticferrite) etc., and does not observe in polygonal ferrite (polygonalferrite).
When being formed to have hot-rolled steel sheet that the ferrite of as above panel construction, tempered martensite and tempering bainite are principal phase, the lath interval of panel construction is narrower, and hot-rolled steel sheet intensity more rises.On the other hand, if lath interval extremely narrows, then hot-rolled steel sheet low-temperature flexibility, stretch characteristics deterioration.Therefore, if only make to have the lath narrower intervals of the ferrite of panel construction, tempered martensite and tempering bainite, then the high strength realizing hot-rolled steel sheet while maintaining high tenacity and excellent stretch characteristics is difficult to.
Therefore, the present inventor etc., to when the lath interval not making to have the ferrite of panel construction, tempered martensite and tempering bainite extremely narrows, guarantee that the means of desired hot-rolled steel sheet intensity are studied.Its result, has found following opinion: not only utilize above-mentioned phase transformation strengthening also to utilize precipitation strength (precipitationstrengthening), and dual-purpose precipitation strength and phase transformation strengthening are extremely effective means.And, the result of further research, there is following opinion: the governing factor (controllingfactor) of precipitation strength is set to the main precipitation relying on Nb, and by adjustment, there is the lath interval of the ferrite of panel construction, tempered martensite and tempering bainite and Nb separates out ratio, can obtain there is desired intensity and the also excellent high tensile hot rolled steel sheet of low-temperature flexibility and ductility.
And then, the present inventor etc. have following opinion, namely, when implementing hot rolling to manufacture hot-rolled steel sheet to the continuous casting slab of the composition with regulation, condition, finish rolling condition is reheated by the cooling of regulation slab, and then in process of cooling after finish rolling terminates, the speed of cooling of regulation thickness of slab middle position, and specify the cooling heat condition again on thickness of slab top layer, thus the hot-rolled steel sheet as described above with desired lath interval and Nb precipitation ratio can be manufactured.
The present invention is based on above opinion and complete, its purport is as follows.
[1] a kind of high tenacity high ductibility high tensile hot rolled steel sheet, it is characterized in that, there is following composition, namely, in mass % containing C:0.04% ~ 0.15%, Si:0.01% ~ 0.55%, Mn:1.0% ~ 3.0%, below P:0.03%, below S:0.01%, Al:0.003% ~ 0.1%, below N:0.006%, Nb:0.035% ~ 0.1%, V:0.001% ~ 0.1%, Ti:0.001% ~ 0.1%, remainder is Fe and inevitable impurity, and have as undertissue, namely, the ratio of the precipitation Nb measured relative to total Nb is 35% ~ 80%, in 1.0mm position, thickness of slab top layer, the tempered martensite that lath interval is 0.2 μm ~ 1.6 μm and/or the volume fraction of tempering bainite are more than 95%, in thickness of slab middle position, the ferritic volume fraction that lath interval is 0.2 μm ~ 1.6 μm is more than 95%.
[2] according to the high tenacity high ductibility high tensile hot rolled steel sheet recorded in above-mentioned [1], it is characterized in that, above-mentioned composition meets following formula (1) and formula (2).
Pcm＝[％C]+[％Si]/30+([％Mn]+[％Cu]+[％Cr])/20+[％Ni]/60+[％V]/10+[％Mo]/7+5×[％B]≤0.25···(1)
Px＝701×[％C]+85×[％Mn]≥181···(2)
At this, in formula (1) and formula (2), the content (quality %) that [%C], [%Si], [%Mn], [%Cu], [%Cr], [%Ni], [%V], [%Mo], [%B] they are each element.
[3] according to the high tenacity high ductibility high tensile hot rolled steel sheet recorded in above-mentioned [1] or [2], it is characterized in that, on the basis of described composition, in mass % further containing Ca:0.0001% ~ 0.005%.
[4] the high tenacity high ductibility high tensile hot rolled steel sheet according to any one of above-mentioned [1] ~ [3], it is characterized in that, on the basis of described composition, one kind or two or more containing what be selected from Cu:0.001% ~ 0.5%, Ni:0.001% ~ 0.5%, Mo:0.001% ~ 0.5%, Cr:0.001% ~ 0.5%, B:0.0001% ~ 0.004% further in mass %.
[5] a kind of manufacture method of high tenacity high ductibility high tensile hot rolled steel sheet, it is characterized in that, continuous casting slab is cooled to less than 600 DEG C, reheat the temperature field to 1000 DEG C ~ 1250 DEG C afterwards, implement roughing and the finish rolling after this roughing, in this finish rolling, make that the draft of non-recrystallization temperature field is 20% ~ 85%, finish rolling end temp is (Ar
3-50 DEG C) ~ (Ar
3+ 100 DEG C) temperature field, after this finish rolling terminates, carry out following cooling: in thickness of slab middle position, less than 750 DEG C and average cooling rate in the temperature field of more than 650 DEG C are 5 DEG C/s ~ 50 DEG C/s, in 1mm position, thickness of slab top layer, after the temperature field cooling being cooled to 300 DEG C ~ 600 DEG C is stopped temperature, reheat to more than 550 DEG C with the time of more than 1s and cool the temperature field starting below temperature, and the cooling of more than 1 time is implemented in the process being again cooled to the temperature field of 300 DEG C ~ 600 DEG C, further, reel at the temperature field of 350 DEG C ~ 650 DEG C; Described continuous casting slab has following composition, namely, in mass % containing C:0.04% ~ 0.15%, Si:0.01% ~ 0.55%, Mn:1.0% ~ 3.0%, below P:0.03%, below S:0.01%, Al:0.003% ~ 0.1%, below N:0.006%, Nb:0.035% ~ 0.1%, V:0.001% ~ 0.1%, Ti:0.001% ~ 0.1%, remainder is Fe and inevitable impurity.
[6] according to the manufacture method of the high tenacity high ductibility high tensile hot rolled steel sheet recorded in above-mentioned [5], it is characterized in that, above-mentioned composition meets following formula (1) and formula (2).
Pcm＝[％C]+[％Si]/30+([％Mn]+[％Cu]+[％Cr])/20+[％Ni]/60+[％V]/10+[％Mo]/7+5×[％B]≤0.25···(1)
Px＝701×[％C]+85×[％Mn]≥181···(2)
At this, in formula (1) and formula (2), the content (quality %) that [%C], [%Si], [%Mn], [%Cu], [%Cr], [%Ni], [%V], [%Mo], [%B] they are each element.
The manufacture method of the high tenacity high ductibility high tensile hot rolled steel sheet [7] recorded in above-mentioned [5] or [6], is characterized in that, on the basis of described composition, in mass % further containing Ca:0.0001% ~ 0.005%.
The manufacture method of the high tenacity high ductibility high tensile hot rolled steel sheet [8] recorded any one of above-mentioned [5] ~ [7], it is characterized in that, on the basis of described composition, one kind or two or more containing what be selected from Cu:0.001% ~ 0.5%, Ni:0.001% ~ 0.5%, Mo:0.001% ~ 0.5%, Cr:0.001% ~ 0.5%, B:0.0001% ~ 0.004% further in mass %.
According to the present invention, be applicable to line-pipes, pipe for oil well use and civil construction steel pipe raw material, the hot-rolled steel sheet from thin-walled to heavy wall of stretch characteristics excellence under intensity, toughness and total thickness can when without the need to containing rare elements or configure new reheating equipment etc. and obtain when maintaining high productivity, industrially exceedingly useful.
Accompanying drawing explanation
Fig. 1 is the figure of the temperature history (thickness of slab middle position and 1mm position, thickness of slab top layer) in the process of cooling after the finish rolling represented in the present invention terminates.
Fig. 2 (a) makes the macrograph (multiplying power: 1000 times) utilizing opticmicroscope to obtain of the hot-rolled steel sheet No.2A (example) of embodiment.Fig. 2 (b) is the macrograph (multiplying power: 20000 times) utilizing transmission type microscope (TEM) to obtain of the hot-rolled steel sheet No.2A (example) of embodiment.
Embodiment
Below, detailed content of the present invention is described.
First, the restriction reason that the one-tenth of high tenacity high ductibility high tensile hot rolled steel sheet of the present invention is grouped into is described.Should illustrate, the % that expression becomes to be grouped into below unless otherwise specified, is the meaning of quality %.
C：0.04％～0.15％
C is lath interval in order to reduce ferrite, tempered martensite and the tempering bainite with panel construction and guarantees the intensity of hot-rolled steel sheet and important element by forming carbide with Nb, V and Ti, in order to meet desired intensity, need to make C content be more than 0.04%.On the other hand, if C content is more than 0.15%, then extremely to narrow at the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite, and due to the excessive increase of precipitate, make the stretch characteristics deterioration under the toughness of hot-rolled steel sheet and total thickness.Meanwhile, carbon equivalent increases, if carry out tubing welding to such hot-rolled steel sheet, then and the toughness deterioration of weld part.Therefore, C content is made to be 0.04% ~ 0.15%.Be more preferably 0.04 ~ 0.10%.
Si：0.01％～0.55％
If the content of Si increases, then become the non-metallic inclusion and reason that toughness of welded zone is worsened that form Mn-Si system.Therefore, Si content with 0.55% for the upper limit.On the other hand, consider from deoxidation effect and steel technological limit processed, the undergage of Si content is decided to be 0.01%.Be more preferably 0.10 ~ 0.45%.
Mn：1.0％～3.0％
Mn is generation in order to suppress polygonal ferrite, guarantee intensity and toughness and the element needed, and in order to play its effect, needs to make Mn content be more than 1.0%.On the other hand, if make Mn content more than 3.0%, then easily produce the deviation (variation) of the mechanical characteristics (mechanicalcharacteristic) with segregation (segregation).In addition, make intensity become too high, then occur the negative impact that stretch characteristics (elongationcharacteristic) reduces etc., and the toughness deterioration of weld part may be made along with the increase of carbon equivalent (carbonequivalent).Therefore, Mn content is made to be 1.0% ~ 3.0%.
Below P:0.03%, below S:0.01%, below N:0.006%
P exists as impurity in steel, is the element of easy segregation, causes the deterioration of the toughness of steel.Therefore, P content using 0.03% as the upper limit.Be more preferably less than 0.02%.
S and N is also same with P, owing to making the toughness deterioration of steel, therefore S content by 0.01%, N content using 0.006% as the upper limit.More preferably S is less than 0.005%.
Should illustrate all there is the limit of the controllability of the steel processed that can realize due to P, S, N, therefore the preferred lower value by P and N is set to 0.001%, the lower value of S is set to 0.0001%.
Al：0.003％～0.1％
Al is used as the reductor (deoxidizingagent) of steel, and Al content is set to and manifests more than 0.003% of deoxidation effect (deoxidationeffect).Wherein, if Al content is excessive, then generates alumina series inclusion, become the reason of the defect of weld part.Therefore, Al content is 0.003% ~ 0.1%.Be more preferably 0.003 ~ 0.06%.
Nb：0.035％～0.1％
Nb to the miniaturization of crystal grain effectively and be precipitation strength element (precipitationstrengtheningelement), in order to ensure the steel strength of X80 level, needs to make Nb content be more than 0.035%.On the other hand, if Nb content is excessive, then when the manufacture of hot-rolled steel sheet, occur excessively to separate out under coiling temperature territory described later (more than 350 DEG C less than 650 DEG C), thus toughness and stretch characteristics are reduced, and make weldability deterioration.Therefore, Nb content is 0.035% ~ 0.1%.Be more preferably 0.035 ~ 0.08%.
V：0.001％～0.1％
V is precipitation strength element, in order to make it effectively play a role, needs to make V content be more than 0.001%.On the other hand, if V content is excessive, then when the manufacture of hot-rolled steel sheet, occur excessively to separate out under coiling temperature territory described later (more than 350 DEG C less than 650 DEG C), thus toughness and stretch characteristics are reduced, and make weldability deterioration.Therefore, V content is made to be 0.001% ~ 0.1%.
Ti：0.001％～0.1％
Ti is effective to the miniaturization of crystal grain, and, being precipitation strength element, in order to manifest its effect, needing to make Ti content be more than 0.001%.On the other hand, if Ti content is excessive, then when the manufacture of hot-rolled steel sheet, there is excessive precipitation thus toughness and stretch characteristics reduction at coiling temperature territory described later (more than 350 DEG C less than 650 DEG C), and make weldability deterioration.Therefore, Ti content is made to be 0.001% ~ 0.1%.Be more preferably 0.001 ~ 0.05%.
High tenacity of the present invention and the high tensile hot rolled steel sheet of high ductibility except mentioned component composition, preferably further containing Ca:0.0001% ~ 0.005%.
Ca：0.0001％～0.005％
Ca suppresses the generation of MnS by fixing S thus has the effect improving toughness.In order to manifest such effect, Ca content is preferably made to be more than 0.0001%.On the other hand, if Ca content is excessive, then owing to forming Ca system oxide compound, toughness is reduced, therefore preferably Ca content is less than 0.005%.Be more preferably 0.001 ~ 0.0035%.
In addition, high tenacity of the present invention and the high tensile hot rolled steel sheet of high ductibility, can be one kind or two or more containing what be selected from Cu:0.001% ~ 0.5%, Ni:0.001% ~ 0.5%, Mo:0.001% ~ 0.5%, Cr:0.001% ~ 0.5%, B:0.0001% ~ 0.004% further except mentioned component composition.
Cu：0.001％～0.5％
Cu is the phase transformation of control steel and improves effective element to the intensity of hot-rolled steel sheet.In order to manifest such effect, Cu content is preferably made to be more than 0.001%.Wherein, the hardening capacity of Cu is strong, if its content is more than 0.5%, then particularly extremely narrow at the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite, stretch characteristics deterioration under toughness and total thickness, and hot workability (hotworkability) may be made to reduce.Therefore, Cu content is preferably made to be 0.001% ~ 0.5%.
Ni：0.001％～0.5％
Ni is the phase transformation of control steel and improves effective element to the intensity of hot-rolled steel sheet.In order to manifest such effect, Ni content is preferably made to be more than 0.001%.Wherein, the hardening capacity of Ni is strong, if its content is more than 0.5%, then particularly extremely narrows at the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite, make the stretch characteristics deterioration under toughness and total thickness, and hot workability may be made to reduce.Therefore, Ni content is preferably made to be 0.001% ~ 0.5%.
Mo：0.001％～0.5％
Mo is the phase transformation of control steel and improves effective element to the intensity of hot-rolled steel sheet.In order to manifest such effect, Mo content is preferably made to be more than 0.001%.Wherein, the hardening capacity of Mo is strong, if its content is more than 0.5%, then particularly extremely narrow at the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite, make the stretch characteristics deterioration under toughness and total thickness, and martensitic generation may be promoted and toughness is reduced.Therefore, Mo content is preferably made to be 0.001% ~ 0.5%.
Cr：0.001％～0.5％
Cr has the carryover effects (delayeffect) of pearlitic transformation (pearlitetransformation) and the minimizing effect of crystal boundary cementite (grainboundarycementite), in order to manifest these effects, Cr content is preferably made to be more than 0.001%.On the other hand, if Cr content is excessive, then particularly extremely narrow at the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite, make the stretch characteristics deterioration under toughness and total thickness.In addition, if Cr content is excessive, then, when tubing welding being carried out to hot-rolled steel sheet, forms quenching structure at weld part, the deterioration of toughness of welded zone may be caused.Therefore, Cr content is preferably made to be 0.001% ~ 0.5%.
Should illustrate, Cu, Ni, Mo and Cr are rare metal, are difficult to stable guarantee and be the element of high price.Therefore, to guarantee from the viewpoint of raw material stable, production cost etc., preferably avoid adding these elements, preferably respective content is less than 0.1% as far as possible.
B：0.0001％～0.004％
B has in the process of cooling when the manufacture of hot-rolled steel sheet after finish rolling terminates and suppresses the ferrite transformation (ferritetransformation) under high temperature and prevent the effect that ferritic hardness reduces.In order to manifest such effect, B content is preferably made to be more than 0.0001%.On the other hand, if B content is excessive, then may form hardened structure (hardenedmicrostructure) at weld part.Therefore, B content is preferably made to be 0.0001% ~ 0.004%.Be more preferably 0.0001 ~ 0.003%.
Preferred high tenacity of the present invention and the high tensile hot rolled steel sheet of high ductibility are formed and meet with the composition of the component target shown in following formula (1) and formula (2).
Pcm＝[％C]+[％Si]/30+([％Mn]+[％Cu]+[％Cr])/20+[％Ni]/60+[％V]/10+[％Mo]/7+5×[％B]≤0.25···(1)
Px＝701×[％C]+85×[％Mn]≥181···(2)
At this, in formula (1) and formula (2), the content (quality %) that [%C], [%Si], [%Mn], [%Cu], [%Cr], [%Ni], [%V], [%Mo], [%B] they are each element.In addition, when steel plate is not containing Cu, [%Cu] in formula (1) is set to zero to calculate Pcm value.[%Cr], [%Ni], [%V], [%Mo], [%B] are too.
Pcm shown in formula (1) is the index of hardening capacity.If Pcm value exceedes certain value, then the tempered martensite as principal phase particularly in thickness of slab skin section and/or the lath interval of tempering bainite extremely narrow, and have the trend of the stretch characteristics deterioration under the toughness of hot-rolled steel sheet and total thickness.Therefore, Pcm value is preferably made to be less than 0.25.Be more preferably less than 0.23.Wherein, if Pcm value becomes too low, then in the welding when tubing or when line pipe lays, produce welding heat affected zone (HAZ) and soften, junction tensile properties may be made to worsen, be therefore preferably more than 0.10.
On the other hand, Px shown in formula (2) is when the manufacture of hot-rolled steel sheet, has the index at the lath interval of the ferrite of panel construction, tempered martensite and tempering bainite at the scope internal control fixture of coiling temperature described later (more than 350 DEG C less than 650 DEG C).In order to reduce lath interval to guarantee the degree of the steel strength of X80 level, Px value is preferably made to be more than 181.Wherein, if Px value becomes too high, then the tempered martensite as principal phase of thickness of slab skin section and/or the lath interval of tempering bainite extremely narrow, and the stretch characteristics under the toughness of hot-rolled steel sheet and total thickness may deterioration, is therefore preferably less than 300.
Should illustrate, in high tenacity of the present invention and in the high tensile hot rolled steel sheet of high ductibility, composition is than that described above Fe and inevitable impurity.As inevitable impurity, such as, Co, W, Pb, Sn etc. can be enumerated.
Next, the restriction reason of the tissue to high tenacity of the present invention and in the high tensile hot rolled steel sheet of high ductibility is described.
High tenacity of the present invention and the high tensile hot rolled steel sheet of high ductibility, separating out the ratio that Nb amount measures relative to total Nb is 35% ~ 80%.In addition, in 1.0mm position, thickness of slab top layer, the tempered martensite that lath interval is 0.2 μm ~ 1.6 μm and/or the volume fraction of tempering bainite are more than 95%, as remainder, can be the ferrite, perlite, martensite and retained austenite etc. of less than 5% containing volume fraction.
In addition, the ferritic volume fraction having 0.2 μm ~ 1.6 μm, lath interval in thickness of slab middle position is the tissue of more than 95%.As remainder, can be the tempered martensite, tempering bainite, perlite, martensite and retained austenite etc. of less than 5% containing volume fraction.
Should illustrate, above-mentioned 1.0mm position, thickness of slab top layer and the martensite of thickness of slab middle position do not comprise island-like martensite.In addition, ferrite is the meaning of polygonal ferrite.In addition, the ferrite with panel construction comprises the ferrite of tip-like ferrite, bainite ferrite, Fei Deman columnar ferrite, acicular ferrite.
Separate out Nb and measure the ratio measured relative to total Nb: 35% ~ 80%
If precipitation ratio is less than 35%, then easily produce undercapacity, and the deviation of mechanical characteristics after tubing becomes large.On the other hand, if more than 80%, then the hardness of ferrite, tempered martensite and tempering bainite rises, and hot-rolled steel sheet toughness and stretch characteristics deterioration, therefore make the upper limit be 80%.
Nb separates out the measuring method of ratio
The ratio (mass ratio) of the Nb separated out in steel plate is determined at the quality of the Nb separated out in steel plate by extraction residue analysis, can try to achieve the ratio (quality %) relative to total Nb content of this measured value.Should illustrate, in extraction residue is analyzed, steel plate is carried out constant current electrolysis (constant-currentelectrolysis) (about 20mA/cm in 10% methyl ethyl diketone (acetylacetone)-1% tetramethylammonium (tetramethylammonium)-methyl alcohol (methanol)
2), by dissolved residue film filter (membranefilter) (aperture: 0.2 μm of φ) trapping, use the mixed flux of sulfuric acid, nitric acid and perchloric acid to melt, utilize ICP luminescence analysis by amount of precipitation quantification.
The principal phase of hot-rolled steel sheet
When manufacture thickness of slab is such as the thick hot-rolled steel sheet of more than 12mm, after hot rolling terminates, if adjustment speed of cooling is to make to generate the ferrite with panel construction in thickness of slab middle position, then the speed of cooling of thickness of slab skin section will extremely become large.Therefore, when forming thick hot-rolled steel sheet, it is extremely difficult for forming the ferrite principal phase tissue with panel construction throughout the whole region of thickness of slab.
Therefore, in the present invention, the principal phase of thickness of slab skin section (from surface of steel plate to the skin section of thickness of slab direction 1.0mm) is formed as tempered martensite and/or the tempering bainite with desired lath interval, on the other hand, the principal phase in the region beyond above-mentioned skin section is formed as having panel construction and there is the ferrite at desired lath interval.Thereby, it is possible to obtain there is high tenacity and the also excellent high tensile hot rolled steel sheet of stretch characteristics under total thickness.
At this, the ferrite that the ferrite with panel construction undergoes phase transition under may be defined as the temperature lower than the temperature generating polygonal ferrite, and observing from the test film that the position of the thickness of slab central part of hot-rolled steel sheet is taked with multiplying power 5000 ~ 20000 times of tem observations or SEM, the ferrite of panel construction can be observed.In addition, the ferrite with panel construction refers to the ferrite comprising tip-like ferrite, bainite ferrite, Fei Deman columnar ferrite, acicular ferrite.
Lath interval: 0.2 μm ~ 1.6 μm
Have the ferrite of panel construction, the lath interval of tempered martensite and tempering bainite is a factor of the intensity affecting hot-rolled steel sheet, therefore needs fineness to a certain degree.But if lath interval is less than 0.2 μm, even if when then not causing Nb etc. to separate out, the hardness of ferrite, tempered martensite and tempering bainite also becomes and rises excessively, and the stretch characteristics deterioration under the toughness of hot-rolled steel sheet and total thickness.On the other hand, if lath interval is more than 1.6 μm, even if when then Nb etc. fully separate out, sufficient hot-rolled steel sheet intensity also cannot be guaranteed, can not meet the steel strength of X80 level.Therefore, lath is made to be spaced apart 0.2 μm ~ 1.6 μm.
The volume fraction of principal phase: more than 95%
In 1mm position, thickness of slab top layer (distance surface of steel plate is in the position of thickness of slab direction 1.0mm), if the total with the desired tempered martensite at lath interval (0.2 μm ~ 1.6 μm) and/or the volume fraction of tempering bainite is less than 95%, then the low-temperature flexibility of thickness of slab skin section significantly reduces.In addition, in thickness of slab middle position, when the ferritic volume fraction with desired lath interval (0.2 μm ~ 1.6 μm) is less than 95%, the low-temperature flexibility in the region beyond thickness of slab skin section significantly reduces.Therefore, in the present invention, make the volume fraction of the principal phase of each position be more than 95%.
Next, the manufacture method of high tenacity high ductibility high tensile hot rolled steel sheet of the present invention is described.
High tenacity high ductibility high tensile hot rolled steel sheet of the present invention can manufacture as follows: the steel billet (slab) with the above-mentioned composition obtained by casting continuously is temporarily cooled or let cool to less than 600 DEG C, after reheating, carry out roughing and finish rolling, under defined terms, carry out accelerating cooling afterwards, reel with specified temperature.
The cooling temperature of continuous casting slab: less than 600 DEG C
When the cooling of steel billet (continuous casting slab) is insufficient, in territory, steel billet top layer, ferrite transformation can not fully complete, and also remains the austenite of non-phase transformation.Like this, if the austenite of residual non-phase transformation, then encourage the grain boundary oxidation generated at austenite grain boundary during casting, the concave-convex surface of the hot-rolled steel sheet obtained increases, and makes the stretch characteristics under total thickness reduce because of nonaffine deformation when load.Therefore, in the present invention, steel billet (continuous casting slab) cooling temperature is made to be less than 600 DEG C that ferrite transformation can fully complete.
That casts slab continuously reheats temperature: 1000 DEG C ~ 1250 DEG C
If billet heating temperature (continuous casting slab reheat temperature) is less than 1000 DEG C, then there is no abundant solid solution as Nb, V and Ti of precipitation strength element and the steel strength of X80 level cannot be guaranteed.On the other hand, if more than 1250 DEG C, then in austenite grain coarsening and cooling after finish rolling terminates and winding process, Nb excessively separates out and makes toughness and the stretch characteristics deterioration of hot-rolled steel sheet.Therefore, the temperature that reheats making continuous casting slab is 1000 DEG C ~ 1250 DEG C.
Steel billet (continuous casting slab) after reheating is adjusted to arbitrary thickness of slab by enforcement roughing and finish rolling.In the present invention, the condition of roughing is not particularly limited.
Draft under non-recrystallization temperature field (no-recrystallizationtemperaturerange) during finish rolling: 20% ~ 85%
By at non-recrystallization temperature field (when steel of the present invention composition, less than about 940 DEG C) carry out finish rolling, the recrystallize of austenite phase postpones and deformation is assembled, the ferrite miniaturization when γ/α phase transformation (γ → α transformation) and intensity and toughness are improved.At this, if the draft under non-recrystallization temperature field during finish rolling is less than 20%, then these effects can not fully manifest.On the other hand, if above-mentioned draft is more than 85%, then resistance to deformation (deformationresistance) increases and plays the effect hindering rolling.Therefore, above-mentioned draft is made to be 20% ~ 85% in the present invention.Be preferably 35% ~ 75%.
Finish rolling end temp: (Ar
3-50 DEG C) ~ (Ar
3+ 100 DEG C)
In order to complete rolling with the particle diameter of homogeneous and tissue, need to make finish rolling end temp be (Ar
3-50 DEG C) more than.If make finish rolling end temp lower than (Ar
3-50 DEG C), then in finish rolling, in steel plate inside, ferrite transformation occurs, tissue becomes uneven and can not get desired characteristic.On the other hand, if finish rolling end temp exceedes (Ar
3+ 100 DEG C), then coarse grains, toughness deterioration.Therefore, finish rolling end temp is made to be (Ar
3-50 DEG C) ~ (Ar
3+ 100 DEG C) scope in.
Should illustrate, finish rolling end temp is the mensuration temperature value of the surface of steel plate of outlet side at finishing mill.
After finish rolling terminates, by cooling and carrying out reeling and obtain hot-rolled steel sheet.In the present invention, the cooling after finish rolling being terminated cools in the mode becoming the temperature history (temperaturehistory) different with thickness of slab surface location from thickness of slab middle position.Fig. 1 is the concise and to the point figure of the temperature history (from finish rolling end temp to the temperature history of coiling temperature) after the finish rolling in the present invention terminates.As shown in Figure 1, coiling temperature is cooled in thickness of slab middle position with the speed of cooling of regulation.On the other hand, at thickness of slab surface location, implement more than 1 time cooling and thermal treatment again, be cooled to coiling temperature afterwards.
Less than 750 DEG C of thickness of slab middle position and the average cooling rate of the temperature field of more than 650 DEG C: 5 DEG C/s ~ 50 DEG C/s
In order to the region beyond thickness of slab skin section suppresses the generation of pearlitic transformation and polygonal ferrite, make the ferritic volume fraction in thickness of slab middle position with panel construction (lath interval: 0.2 μm ~ 1.6 μm) be more than 95% and guarantee toughness, the average cooling rate needing the temperature field of less than 750 DEG C more than 650 DEG C made in thickness of slab middle position is 5 DEG C/more than s.Wherein, if become excessive in the cooling rate of this thickness of slab middle position, then the lath interval with the ferrite of panel construction, tempered martensite and tempering bainite extremely diminishes, and stretch characteristics is deteriorated, therefore needs to make the upper limit be 50 DEG C/s.
1mm position, thickness of slab top layer: cooling and thermal treatment again
In the present invention, in order to control the volume fraction of the tempered martensite and/or tempering bainite in 1.0mm position, thickness of slab top layer with desired lath interval (0.2 μm ~ 1.6 μm) to count more than 95%, under needing the state being defined as above-mentioned scope in the speed of cooling of thickness of slab middle position, process below 1mm position, thickness of slab top layer is implemented.This is treated to, temperature from accelerating cooling is until the cooling of the temperature field of 300 DEG C ~ 600 DEG C stops temperature (once cooling stops temperature) with after any speed of cooling cooling, make it reheat to more than 550 DEG C with more than 1 second (single reheat time) and cool the temperature field (single reheat temperature) starting below temperature, again be cooled to the process of the temperature field of 300 DEG C ~ 600 DEG C, need enforcement more than 1 time this process before being reeled up.At this, temperature is stopped to be set to cooling when implementing n this process cooling for n time stopping temperature, the reheating time to be set to n reheating time, reheat temperature and to be set to n reheat temperature.The regulation reason of each controlling factor is as follows.
N cooling stops temperature: 300 DEG C ~ 600 DEG C
The object of present treatment is, on distance surface until temporarily form low temperature phase change tissue (martensitic stucture and/or bainite structure) in the skin section (thickness of slab surface region) of thickness of slab direction 1.0mm, carries out tempering by reheating to it.Thus, regulate the lath interval of tempered martensite in thickness of slab skin section and/or tempering bainite, the stretch characteristics under surface hardness and total thickness can be improved.When cooling stops temperature more than 600 DEG C, organize due to low temperature phase change and fully do not generate, therefore thickness of slab skin section can not be formed tempered structure, and the stretch characteristics under total thickness reduces.On the other hand, n cooling stops temperature when being less than 300 DEG C, can not reach target reheat temperature, and having difficulty cannot fully tempering, the stretch characteristics reduction under total thickness.
N reheat temperature: more than 550 DEG C and cooling start below temperature
When reheat temperature is less than 550 DEG C, can not to organize abundant tempering and rise in the hardness of thickness of slab skin section, stretch characteristics under total thickness reduces.On the other hand, if reheating (reheating) temperature exceedes cooling start temperature (usually, finish rolling end temp-20 DEG C ~ finish rolling end temp), then occur from ferrite to austenitic reverse transformation (reversetransformation) in thickness of slab skin section, when again cooling, form hardened structure.Its result, produce rise in the hardness of thickness of slab skin section, problem that stretch characteristics under total thickness reduces and so on.Therefore, reheat temperature is more than 550 DEG C and cools the temperature field starting below temperature.
N the reheating time: more than 1 second
The reheating time is when being less than 1 second, can not to organize abundant tempering and rise in the hardness of thickness of slab skin section, stretch characteristics under total thickness reduces.Therefore, the reheating time is made to be more than 1 second.Wherein, if the reheating time becomes long, then as a result, reheat temperature uprises, so occur from ferrite to austenitic reverse transformation in thickness of slab skin section, when again cooling, forms hardened structure.Therefore, may rise in the hardness of thickness of slab skin section, stretch characteristics under total thickness reduces and production efficiency significantly reduces.From the viewpoint, the reheating time is preferably made to be less than 5 seconds.
Be cooled to coiling temperature after above-mentioned reheating, or after the temperature field (300 DEG C ~ 600 DEG C) being cooled to above-mentioned cooling stopping temperature, repeatedly carry out the process of reheating with the cycle specified, be cooled to coiling temperature afterwards.
Should illustrate, as under the state that the speed of cooling in thickness of slab middle position is defined in above-mentioned scope, cooling heat treated means again desired by implementing in 1mm position, thickness of slab top layer, such as, can utilize intermittent cooling (intermittentcooling).In addition, except intermittent cooling, induction heating equipment can also be configured between cooling tank, use it top layer to be heated to the means such as the reheat temperature specified.
Coiling temperature: 350 DEG C ~ 650 DEG C
In order to utilize the precipitation strength based on precipitates such as Nb, V, Ti, need to make coiling temperature be more than 350 DEG C.In order to make above-mentioned precipitate especially effectively separate out, coiling temperature is preferably made to be more than 400 DEG C.On the other hand, if coiling temperature is more than 650 DEG C, then due to the amplification at the lath interval of the coarsening of precipitate, the ferrite with panel construction, tempered martensite and tempering bainite, intensity is reduced.In addition, if coiling temperature is more than 650 DEG C, then generates thick perlite and make toughness deterioration, therefore the upper limit is set to 650 DEG C.Be preferably 400 DEG C ~ 650 DEG C.Should illustrate, coiling temperature is the temperature of surface of steel plate.But the temperature of this temperature and 1mm position, thickness of slab top layer is almost equal.
Should illustrate, in the present invention, the component segregation of steel during in order to reduce continuous casting, can use induction stirring (EMS:electro-magneticstirrer), slighter compress to cast (IBSR:intentionalbulgingsoftreductioncasting) etc.By implementing induction stirring process, equiax crystal (equiaxedcrystal) can be formed at thickness of slab central part, segregation is reduced.In addition, when implementing slighter compress casting, by preventing the flowing of the molten steel in the portion of not solidifying casting steel billet continuously, the segregation of thickness of slab central part can be reduced.Even if these segregations reduce process less, by using one, the absorption energy (vE in Charpy impact test described later also can be made
-60dEG C), ductility-brittle rupture transition temperature (vTrs) and DWTT characteristic become more excellent grade.
Embodiment
Use steel billet (the continuous casting slab of the composition shown in table 1, wall thickness: 215mm), hot rolling is implemented under hot-rolled condition shown in table 2, cool under cooling conditions after hot rolling terminates shown in table 2, be wound into spirrillum with the coiling temperature shown in table 2, form the hot-rolled steel sheet (steel band) of the thickness of slab shown in table 2.When casting continuously, about the steel plate beyond the steel plate No.1G in table 2 ~ 4 described later, in order to the segregation carrying out composition reduces process, carry out induction stirring (EMS).Should illustrate, for the cooling after hot rolling terminates, by carrying out intermittent cooling thus being adjusted to each cooling conditions shown in table 2.
From the hot-rolled steel sheet obtained, take test film, implement structure observation, extraction residue analysis, tension test, shock test, DWTT test and hardness test by the following method.
(1) structure observation
The block test sheet (blockishtestspecimen) can observing whole position, thickness of slab direction is taked from the hot-rolled steel sheet obtained, use sweep electron microscope (multiplying power: 2000 ~ 5000 times), implement L cross-section (hot-rolled steel sheet width is vertical with sightingpiston).In order to obtain the average information of tissue, to thickness of slab 1/2 (central authorities) position, 1mm position, thickness of slab top layer, observing in each thickness of slab position and taking 3 visuals field.Use like this by observing and the macrograph taken more than 3 visuals field and obtain, the each area ratio formed shared by tissue (there is the ferrite of panel construction, tempered martensite and tempering bainite) relative to observing visual field area is tried to achieve by image analysis (imageanalysis), and using these mean values as each volume fraction forming tissue.
In addition, film sample (thin-filmsample) is taked from the thickness of slab middle position of the hot-rolled steel sheet obtained and 1mm position, top layer, use transmission type microscope (multiplying power: 20000 times), for each thickness of slab position, observe and take the lath boundaries more than 4 in more than 3 visuals field position arranged in parallel.And then, measure from the observable whole lath interval of the respective photo obtained, try to achieve the mean value at whole lath interval of mensuration, try to achieve the ferritic lath interval that is positioned at thickness of slab middle position thus and be positioned at the tempered martensite of 1mm position, top layer and the lath interval of tempering bainite.Be evaluated as at " the lath interval that intensity, toughness, stretch characteristics are good " time in scope lath being spaced apart 0.2 μm ~ 1.6 μm.
(2) extraction residue analysis (separating out the measuring method of Nb ratio)
Take test film by the thickness of slab middle position of the hot-rolled steel sheet obtained and each position of 1mm position, top layer, be determined at the quality of the Nb separated out in steel plate (test film) by extraction residue analysis.Should illustrate, in extraction residue is analyzed, with 10% methyl ethyl diketone-1% tetramethylammonium-methyl alcohol, constant current electrolysis (about 20mA/cm be carried out to steel plate (test film)
2), trap dissolved residue with film filter (aperture: 0.2 μm of φ), use the mixed flux of sulfuric acid, nitric acid and perchloric acid to melt, dilute with water is a certain amount of thus with ICP luminescence analysis, Nb is separated out ratio quantification.Ratio of being separated out by Nb is " the Nb precipitation ratio that intensity, toughness, stretch characteristics are good " in thickness of slab middle position and 1mm position, the top layer average evaluation be in the scope of 35% ~ 80%.
(3) tension test
To make the direction (C direction) orthogonal with rolling direction for long side direction, flat total thickness tension test sheet (thickness of slab: total thickness is taked from the hot-rolled steel sheet obtained, parallel portion length: 60mm, gauge length: 50mm, gauge length portion width: 38mm), be defined as foundation with ASTME8M-04, at room temperature implement tension test, try to achieve yield strength YS, tensile strength TS, entirely stretch EL.Be more than 550MPa by yield strength, tensile strength be more than 650MPa, percentage of total elongation be more than 20% average evaluation be " tensile properties is good ".But if intensity becomes too high, then stretch characteristics reduces, therefore preferably yield strength is below 690MPa, tensile strength is below 760MPa.
(4) Charpy impact test (Charpyimpacttest)
V notch test sheet (V-notchedtestbar) (length 55mm × height 10mm × width 10mm) is taked from the thickness of slab middle position of the hot-rolled steel sheet obtained for long side direction to make the direction (C direction) orthogonal with rolling direction, being defined as according to implementing Charpy impact test with JISZ2242, tries to achieve test temperature: the absorption at-60 DEG C can (absorbedenergy) (J) and ductility-brittle fracture surface transition temperature (ductile-brittlefracturesurfacetransitiontemperature) (DEG C).Should illustrate, test film is set to 3, obtaining the absorption that obtains can the arithmetical av of value and ductility-brittle fracture surface transition temperature, and the absorption being set to this steel plate can value (vE
-60) and ductility-brittle fracture surface transition temperature (vTrs).By vE
-60the average evaluation being less than-80 DEG C for more than 100J, vTrs is " toughness is good ".
(5) DWTT test
To make the direction (C direction) orthogonal with rolling direction for long side direction, DWTT test film (size: thickness of slab total thickness × width 3in. × length 12in.) is taked from the hot-rolled steel sheet obtained, foundation is defined as with ASTME436, carry out DWTT test, try to achieve the minimum temperature (DWTT) that ductility surface of fracture rate (shearfracturepercentage) is 85%.Be that the average evaluation of less than-30 DEG C is for having " excellent DWTT characteristic " by DWTT.
(6) hardness test
From the hot-rolled steel sheet obtained, take the block test sheet (size: thickness of slab total thickness × width 10mm × length 10mm) of measurement of hardness, use Vickers pyramid hardness testing machine, be determined at the hardness of 1mm position, thickness of slab top layer with 1.0kg load.
The result of above-mentioned (1) ~ (6) is shown in table 3 and table 4.
[table 3]
* 4) contained in hot-rolled steel sheet precipitation Nb measures the ratio measured relative to total Nb
* 5) F: the ferrite TM with panel construction: tempered martensite TB tempering bainite
* 6) total of the volume fraction of tempered martensite (TM) and the volume fraction of tempering bainite (TB)
* 7) due to quenching or tempering insufficient, so major part is martensite and/or bainite structure
[table 4]
* 8) ductility-brittle fracture surface transition temperature
* 9)-60 DEG C time absorption energy
As shown in Table 3 and Table 4, the hot-rolled steel sheet of example does not observe skin section over-curing, and tensile properties (intensity, ductility) and toughness (low-temperature flexibility) all good.On the other hand, for the hot-rolled steel sheet of comparative example, either one or both of tensile properties and toughness (low-temperature flexibility) can not get sufficient characteristic.
Fig. 2 (a) and Fig. 2 (b) is the result of the same test film that the thickness of slab middle position of the hot-rolled steel sheet (steel plate: 2A) of the example that structure observation is recorded from table 2 ~ 4 is taked.Fig. 2 (a) is the macrograph based on observation by light microscope (multiplying power: 1000 times), and Fig. 2 (b) is the macrograph based on tem observation (multiplying power: 20000 times).In Fig. 2 (a), do not observe the panel construction of ferrite, tempered martensite and tempering bainite.But, in Fig. 2 (b), can confirm there is the panel construction of ferrite, tempered martensite and tempering bainite (this photo is ferrite).Should illustrate, the arrow in Fig. 2 (b) represents lath interval.
Claims (8)
1. a hot-rolled steel sheet, it is characterized in that, there is following composition: in mass % containing C:0.04% ~ 0.15%, Si:0.01% ~ 0.55%, Mn:1.0% ~ 3.0%, below P:0.03%, below S:0.01%, Al:0.003% ~ 0.1%, below N:0.006%, Nb:0.035% ~ 0.1%, V:0.001% ~ 0.1%, Ti:0.001% ~ 0.1%, remainder is Fe and inevitable impurity, and having as undertissue: the ratio that the precipitation Nb measured relative to total Nb measures is 35% ~ 80%, in 1.0mm position, thickness of slab top layer, lath is spaced apart the tempered martensite of 0.2 μm ~ 1.6 μm and/or the volume fraction of tempering bainite is more than 95%, in thickness of slab middle position, the ferritic volume fraction that lath is spaced apart 0.2 μm ~ 1.6 μm is more than 95%.
2. hot-rolled steel sheet according to claim 1, is characterized in that, described composition meets following formula (1) and formula (2),
Pcm＝[％C]+[％Si]/30+([％Mn]+[％Cu]+[％Cr])/20
+[％Ni]/60+[％V]/10+[％Mo]/7+5×[％B]≤0.25···(1)
Px＝701×[％C]+85×[％Mn]≥181···(2)
Wherein, in formula (1) and formula (2), the content that [%C], [%Si], [%Mn], [%Cu], [%Cr], [%Ni], [%V], [%Mo], [%B] they are each element, in mass %.
3. hot-rolled steel sheet according to claim 1 and 2, is characterized in that, on the basis of described composition, in mass % further containing Ca:0.0001% ~ 0.005%.
4. the hot-rolled steel sheet according to any one of claims 1 to 3, it is characterized in that, on the basis of described composition, one kind or two or more containing what be selected from Cu:0.001% ~ 0.5%, Ni:0.001% ~ 0.5%, Mo:0.001% ~ 0.5%, Cr:0.001% ~ 0.5%, B:0.0001% ~ 0.004% further in mass %.
5. the manufacture method of a hot-rolled steel sheet, it is characterized in that, after the continuous casting slab formed as follows is cooled to below 600 DEG C, reheat the temperature field to 1000 DEG C ~ 1250 DEG C, implement roughing and the finish rolling after this roughing, in this finish rolling, make that the draft of non-recrystallization temperature field is 20% ~ 85%, finish rolling end temp is (Ar
3-50 DEG C) ~ (Ar
3+ 100 DEG C) temperature field, after this finish rolling terminates, carry out following cooling: in thickness of slab middle position, less than 750 DEG C and average cooling rate in the temperature field of more than 650 DEG C are 5 DEG C/s ~ 50 DEG C/s, in 1mm position, thickness of slab top layer, after the temperature field cooling being cooled to 300 DEG C ~ 600 DEG C is stopped temperature, reheat to more than 550 DEG C with the time of more than 1s and cool the temperature field starting below temperature, and the cooling of more than 1 time is implemented in the process being again cooled to the temperature field of 300 DEG C ~ 600 DEG C, and, reel at the temperature field of 350 DEG C ~ 650 DEG C
Wherein, consisting of of described continuous casting slab contains C:0.04% ~ 0.15%, Si:0.01% ~ 0.55%, Mn:1.0% ~ 3.0%, below P:0.03% in mass %, below S:0.01%, Al:0.003% ~ 0.1%, below N:0.006%, Nb:0.035% ~ 0.1%, V:0.001% ~ 0.1%, Ti:0.001% ~ 0.1%, remainder is Fe and inevitable impurity.
6. the manufacture method of hot-rolled steel sheet according to claim 5, is characterized in that, described composition meets following formula (1) and formula (2),
Pcm＝[％C]+[％Si]/30+([％Mn]+[％Cu]+[％Cr])/20
+[％Ni]/60+[％V]/10+[％Mo]/7+5×[％B]≤0.25···(1)
Px＝701×[％C]+85×[％Mn]≥181···(2)
At this, in formula (1) and formula (2), the content that [%C], [%Si], [%Mn], [%Cu], [%Cr], [%Ni], [%V], [%Mo], [%B] they are each element, in mass %.
7. the manufacture method of the hot-rolled steel sheet according to claim 5 or 6, is characterized in that, on the basis of described composition, in mass % further containing Ca:0.0001% ~ 0.005%.
8. the manufacture method of the hot-rolled steel sheet according to any one of claim 5 ~ 7, it is characterized in that, on the basis of described composition, one kind or two or more containing what be selected from Cu:0.001% ~ 0.5%, Ni:0.001% ~ 0.5%, Mo:0.001% ~ 0.5%, Cr:0.001% ~ 0.5%, B:0.0001% ~ 0.004% further in mass %.
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| US (1) | US10287661B2 (en) |
| EP (1) | EP2949772B1 (en) |
| JP (1) | JP5679091B1 (en) |
| KR (1) | KR101728789B1 (en) |
| CN (1) | CN105121684B (en) |
| BR (1) | BR112015023632B1 (en) |
| WO (1) | WO2014162680A1 (en) |
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Also Published As
| Publication number | Publication date |
|---|---|
| BR112015023632B1 (en) | 2020-04-28 |
| US10287661B2 (en) | 2019-05-14 |
| KR20150122779A (en) | 2015-11-02 |
| CN105121684B (en) | 2017-03-15 |
| EP2949772A1 (en) | 2015-12-02 |
| KR101728789B1 (en) | 2017-04-20 |
| US20160017466A1 (en) | 2016-01-21 |
| EP2949772B1 (en) | 2019-06-19 |
| EP2949772A4 (en) | 2016-06-01 |
| BR112015023632A2 (en) | 2017-07-18 |
| JPWO2014162680A1 (en) | 2017-02-16 |
| WO2014162680A1 (en) | 2014-10-09 |
| JP5679091B1 (en) | 2015-03-04 |
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